I’ve used UV LED’s to build a PCB exposure unit, and that was very successful, so I thought I would see if a UV LED could be used to erase an EPROM.As experiments go, it was rather a long shot. The UV LEDs I’ve got emit UV light at a wavelength of around 400nm, and EPROMs need to be exposed to UV light at around 250nm. However UV is UV so it was worth a try.It didn’t work :(In the end, it had around five hours of exposure and after reading back the EPROM contents, not even one bit had changed state. Still, I suppose it’s nice to know.

I’ve been working on some switch boxes for work over the last couple of days. I’ve got to build six of them and whilst they look complicated, they are really quite simple as there are no real electronics inside; just a lot of switches, LEDs, current limiting resistors and a couple of power diodes. However, some of the wiring needed to be capable of comfortably handling around 8 to 10 amps, so I had to go routing in the back of my cable cupboard to see what I had. I’ve acquired a lot of reels of cable over the years for various projects, and some of the reels weren’t labelled with their specifications other than just the cable size. I found some information on the web that gives a rule of thumb for converting cable sizes to amp carrying capacity, and I’ve placed it in my technical documents section for those that may find it useful.

One of six switch boxs - this one is being tested before it gets it's labels.

I’ve created a new tech tip article on the method I use for creating double-sided PCB’s for those that are interested. It’s really not that difficult and doesn’t require any special hardware, just a little bit of patience and care. Enjoy.

Simple answer... Yes... Less simple answer... usually...Now it’s true that you get what you pay for when it comes to tools, but some tools don’t seem to last irrespective how much you pay for them.The humble wire-cutters, a basic item that should be in every hobbyists tool box, and an item you can spend a lot of money on, however, often cheaper is better value.Wire-cutters come in all shapes and sizes and a pair with an overall length of around 125mm are idea for hobby electronics work, and a pair of these will cost you anywhere from £2.50 to over £100. I seem to go through around two to three pairs of wire-cutters a year and it doesn’t seem to matter how much I pay for them. So, how do you know if you need a new pair of cutters? Well that’s simple, hold them up to a light and look how the jaw blades meet.

The above image shows a new pair of cutters on the left, and a used pair on the right. You can see little dinks in the blades that let though light. These will make bad cuts and you notice this when clipping off component leads for example. When the cutters are new, the component lead will usually shoot off as you clip it. However, when the blades are worn or damaged they start to crimp the component lead as opposed to cutting it meaning you have to work harder and your cuts aren’t as clean.

The simple way to damage a pair of wire cutters is to cut either wire that is too thick; don’t use them to cut heavy gauge mains type cable, or cut things other than wire, and this applies no matter how much you pay for your cutters.If you find you need to cut heavy gauge wire, invest in an electricians pair of wire cutters or even a pair of cable shears for the really heavy gauge stuff.

Another great way to destroy a pair of cutters, is to try and use them (an old pair thank heavens) to cut into a plastic box.

Well, I'm making progress on my PIC programmer. This has been one of those projects that has been overly difficult and problematic for no apparent reasons. I had problems with some of the switches with built-in LED’s I’ve been using; a couple of them were faulty and that caused me some head scratching for a while. Then my current PIC programmer would work with my PC at all; for some reason the USB card in the PC had come lose but again, I spent a fair amount of time re-booting the PC and messing around. Needless to say all the other USB devices that are plugged into the other USB ports were working fine. I then had problems getting the PIC (there’s a PIC at the core of my new programmer) to work correctly. For some reason the results were very intermittent and I was getting worried that the design was fundamentally flawed, but it turned out that there’s an “issue” with the AMICUS compiler which I need to report to the manufacturer. This really should have been a weekend type project instead it’s been dragging on for several weeks. However, I managed to get one of it’s channels up and working yesterday and it worked perfectly, so now I just need to etch a couple of additional boards for the remaining programming channels, and then create some interconnect cables and it’s done.